Xray detection
Xray detection
(OP)
I have a question. I have a successful photodetector circuit with 8-bit resolution from an on mcu adc. works well from a dark room to room well lit. The detection comes from a simple 1n4148 glass encased diode a couple of op amps to give a dc offset for low readings and approximatley 100 times gain. QUESTION: What would have to occur to make this an Xray detector. The radiation is in the medical diagnostic range 50kVp - 120kVp. The circuit will do nothing in the radiation beam and my thoughts would be it should register full on the same circuit as the photodetector; higher frequency beam higher energy and therefore a higher reading on the same circuit.
Any suggestion greatly appreciated; XRAY
Any suggestion greatly appreciated; XRAY





RE: Xray detection
You could potentially wrap the diode with some sort of X-ray scintillating material. Do a web search on x-ray scintillator.
TTFN
RE: Xray detection
Hope this helps a bit..
RE: Xray detection
RE: Xray detection
Not that I have any practical answers for you.
RE: Xray detection
RE: Xray detection
Point of fact is also that Si is essentially transparent in x-ray regime, as fluoroscopes are often used to inspect die bonds, which require the intervening material to be reasonably transparent in the x-ray regime.
Most standard Si x-ray detectors use a fluorescing material to convert the signal to a visible signal.
TTFN
RE: Xray detection
So far as "blasted away": far enough away that it's probably not gonna be recaptured by the atom. Same as any ion -- it's just short an electron. Kind of like a missle that reaches escape velocity, it's just gone for good.
You're talking a difference of 5 magnitudes. That's huge. Imagine the difference between a 1hp motor and a 100,000hp motor. No comparison. Trying to detect x-rays with a silicone diode is like using a bathroom scale to weigh an elephant, or using an AM radio to detect visible light.
RE: Xray detection
RE: Xray detection
http://www.eng.auburn.edu/~troppel/courses/elec663spring2000/OralPresentations/Pres_Li_Ying.ppt
or
http://www.microsemi.com/brochures/pindiodes/appendix%20f.pdf
The electron drift detector seems to be a similar concept but in a very different configuration:
http://www.ketek.net/layer2/products/1comm_x_ray1.htm
This is an interesting site on x-ray detection in general:
http://www.canberra.com/literature/basic_principles/gamma.htm
X-ray fluorescence of visible light (XRF) might work for you, but I couldn't find any goon on-line information on what would be a suitable material.
RE: Xray detection
Is the diode in a light tight package. If not the visible photon flux will mask the x-ray output.
Is the window in front of the detector low Z so that the x-rays can penetrate it?
what is your source of x-rays. An x-ray tube will provide a good flux and should be detected. a smoke detector source is not intense enough to produce much signal.
RE: Xray detection
working for a company called Black Forest Engineering.
The project was for a company called Cardiac Mariners.
I'm sure you can find information on both of these
companies. To get to the point ... this system used
a compound of Cadmium Telluride. This compound was very
good at producing a lot of detectable current from just
one high-energy x-ray photon.
RE: Xray detection
Pin diodes are used for detecting x-rays all the time.
You can get more than one electron per x-ray.
In fact I have a pin diode detector in my office
that can measure the energy of the x-rays by
measuring how many electrons are produced by
a single x-ray.
However, it takes a lot of low-noise expertese
to detect one x-ray at a time. As you move to
medical type hard x-rays the absorption of the
silicon drops, so you detect fewer of the x-rays
flying through the silicon. But at the kind of fluxes
that medical x-rays use, you should be able to
detect a signal.
A scintillator on top of the diode can get you much more signal
because they produce light, and because they
are thicker and have higher absorption.
Almost any phosphor will detect x-rays, as
will some fluorescent plastics. The common
scintillator used for this purpose is thallium
doped sodium iodide.
Best regards
mark
RE: Xray detection